Pipe stream throws error: response has been emitted already

[Borewit]

Describe the bug

Pipe stream causes error: "The response has been emitted already."

Blocks: sindresorhus/file-type#470

• got version v11.8.2
• Node.js version: 16.4.2
• OS & version: Windows 10

Actual behavior

Throws an error

C:\Users\Maarten\code\github\got\dist\source\core\index.js:1476
            throw new Error('Failed to pipe. The response has been emitted already.');
                  ^

Error: Failed to pipe. The response has been emitted already.
    at Request.pipe (C:\Users\Borewit\code\github\got\dist\source\core\index.js:1476:19)
    at Request.<anonymous> (C:\Users\Borewit\code\github\examples\examples\file-type\got-error.js:9:14)
    at Object.onceWrapper (node:events:513:28)
    at Request.emit (node:events:394:28)
    at emitReadable_ (node:internal/streams/readable:571:12)
    at processTicksAndRejections (node:internal/process/task_queues:82:21)

Expected behavior

Be able to read the HTTP content using a stream.
I don't see what reading has to do with HTTP headers already sent (emitted).

Code to reproduce

const got = require('got');
const stream = require('stream');

const url = 'https://upload.wikimedia.org/wikipedia/en/a/a9/Example.jpg';

const httpStream = got.stream(url);
httpStream.on('error', error => console.error(error));
httpStream.once('readable', async () => {
  httpStream.pipe(new stream.PassThrough());
});
...

Checklist

• I have read the documentation.
• I have tried my code with the latest version of Node.js and Got.

Workaround

See: dec028d

[Borewit]

I checked out version 11.8.2 and created (branch from there)[https://github.com/Borewit/got/tree/issue-1803-prevent-emitted-already-error].

Interesting enough this the 11.8.2, respectively commit f896aa5 seems not to (no longer) belong to this repo...

[szmarczak]

You can replace

if (this[kStartedReading]) {

with

if (this[kStartedReading] && this.listenerCount('data') > 0) {

If that doesn't help then Got does everything correctly here. You cannot use a response once it has been used already. Let me know if that change fixes the issue.

[szmarczak]

I think that this might cause the issue.

[szmarczak]

Hmm... this.listenerCount('data') may not be the ideal approach, but I don't think we have a better shot at detecting already-used responses...

[szmarczak]

This should fail:

import got from './dist/source/index.js';
import stream from 'stream';

const url = 'https://upload.wikimedia.org/wikipedia/en/a/a9/Example.jpg';

const httpStream = got.stream(url);
httpStream.on('error', error => console.error(error));
httpStream.once('readable', async () => {
+ httpStream.read();
  httpStream.pipe(new stream.PassThrough());
});

[szmarczak]

If you want to re-use the stream (e.g. return it) then you need to restore what you have read.

Ah, you're returning the pass stream, not the Got one... So this seems right. Sorry for confusion.

[szmarczak]

Let's remove the check entirely. Maybe undici will prevent response reuse. Our check works incorrectly.

[szmarczak]

Will be released in the next beta, thanks for reporting.

[Borewit]

Thanks for your swift response & fix @szmarczak !

[szmarczak]

@Borewit Released second beta :)